Your body’s immune system normally fights illness or injury, but when it’s overactive over a prolonged period of time, the consequences can be harmful. “Chronic systemic inflammation” (marked by raised levels of pro-inflammatory cytokines through the body) has been linked to a wide range of physical and mental health problems, including heart disease, diabetes and depression. One cause is a poor lifestyle, involving little exercise and an unhealthy diet. Anthony Ong, at Cornell University, US, and his team were interested in whether our emotional lives might play a role too. Their new research, published in the journal Emotion, found that people with lower systemic inflammation didn’t simply report more happiness, rather they experienced a greater variety of positive emotions every day.

“There’s growing evidence that inflammatory processes may help to explain how emotions get ‘under the skin,” the researchers write in their paper. They point to evidence suggesting that negative emotions, such as fear and shame, can stimulate inflammatory responses. And also to work finding that positive emotions are associated with lower levels of C-reactive protein and IL-6 (two classic markers of inflammation). “Taken together, experiences of negative and positive emotion in both trait and state form appear to influence the adaptive regulation of core biological systems that maintain health,” they write.

The team analysed previously-collected data on 175 healthy people aged 45-60 living in Phoenix, Arizona. These volunteers had their levels of three inflammatory markers (IL-6, CRP and fibrinogen) measured at the start of the study, and at a six-month follow-up. They were also taught how to use a tablet computer to provide questionnaire-led diary entries each night for 30 days.

The questions included a measure of daily emotional experiences: the volunteers were asked to rate the extent to which they’d experienced 16 positive emotions (including feeling enthusiastic, determined or amused), and 16 negative emotions (including feeling afraid, distressed, jittery, anxious or ashamed) during that day.

When the team analysed the data, they found that greater positive “emodiversity” – regularly experiencing a broad range of positive emotions – was associated with lower levels of inflammation (this was after they’d controlled statistically for any influences of age, gender, medications, BMI, medical conditions and personality). There was, however, no significant relationship between negative emodiversity and inflammation. “These findings highlight the unique role daily positive emotions play in biological health,” the researchers conclude.

There were limitations with the study. Volunteers were asked to remember at night all the different emotions they’d experienced in the course of the day. Since chronic inflammation is also associated with poorer memory, it’s possible that people with elevated inflammation just couldn’t remember all their emotional experiences. Studies using a more intensive emotion sampling approach could provide more useful results.

It’s also impossible, from this study, to answer the question: how could experiencing a diverse spectrum of positive emotions influence inflammation? It’s possible that being more in tune with exactly how you’re feeling could lead to more adaptive health behaviours, the researchers suggest.

But as they also concede, “the directionality of the observed associations cannot be determined.” It might be that a lack of diversity in emotion results from heightened levels of inflammation, rather than causes them. Certainly, when it comes to depression, for example, while raised levels of inflammatory markers are associated with depression, whether that’s a result or a cause is debated. Clearly, there’s a need for good longitudinal studies to clarify these relationships.